This application claims the priority of PCT International Application No. PCT/EP99/09237, filed Nov. 27, 1999 and German patent document 198 57 394.4, filed Dec. 12, 1998, the disclosures of which is expressly incorporated by reference herein.
The invention relates to a regulatable suspension system for an active chassis of a motor vehicle.
German patent document DE 44 38 929 C1 discloses a hydraulic steering actuator for a parameter-dependently controlled vehicle steering arrangement, comprising a steering lever which is arranged on a steerable wheel and which is connected to the piston rod of a hydraulic steering actuator. The steering actuator is set by means of actuating signals which are generated in a computer as a function of various parameters, for example the rotary position of the steering wheel, the traveling speed or the yaw velocity of the vehicle. The steering actuator can be set in a regulated manner as a result of a desired-value/actual-value comparison between measured and calculated state variables.
Furthermore, various kinds of suspension systems for motor vehicles are known, which comprise a plurality of components, such as spring, damper and links, and which make it possible to influence the possible movements of the wheel, in particular steering angle, stroke, camber and toe in an active or passive manner as intended.
For safety reasons, the greatest possible functioning capacity of the components determining the steering must be ensured. Particularly in the case of drive-by-wire systems, in which there is no direct mechanical transfer of the driver's steering movement to the steered wheels, an operating failure in the steering transmission path must be remediable by means of a usually redundant design. This results, however, in increased production, assembly and operating costs of the suspension systems; moreover, redundantly designed suspension systems require more construction space.
One object of the invention is to provide a regulatable suspension system for an active chassis, which ensures a high degree of safety and flexibility in a simple manner.
This and other objects and advantages are achieved by the suspension system according to the invention, in which redundancy is achieved by providing at least two actuators that act upon the wheel and generate actuating movements or actuating vectors which have parallel direction components. This is achieved by providing an angle other than 90.degree. between the actuating directions of the two actuators, so that the effective directions of the two actuators are at least partially superposed on one another. Thus, when there is a fault due to a defect of one actuator, the function of the latter can be at least partially performed by the second actuator.
The operating state of the actuators is checked regularly via a control unit and, when a failure of one actuator is detected, actuating signals acting upon the remaining (intact) actuator are generated. These actuating signals cause the intact actuator to perform the function of the defective actuator, by intensifying the actuating movement of the intact actuator or to adapting it in the effective direction of the defective actuator until the function of the defective actuator is performed completely or partially.
This novel concept achieves a reduction of the number of components in the suspension system, because it is no longer necessary to provide a replacement actuating element for each actuator in order to ensure the necessary operating reliability. Instead, it is possible to achieve redundancy for a plurality of actuators using only a single additional actuator which performs additional functions that correspond to the primary functions of the other actuators. Furthermore, a graded safety strategy can be implemented, in which only those actuators that are particularly relevant to safety are protected redundantly.
In one embodiment of the invention, the actuating direction of the additional actuator has a direction component which runs parallel to the actuating direction of at least two further actuators. In the event of a fault, the additional actuator can perform the function of the defective actuator, so that it is possible to ensure a safeguard against the operating failure of at least two actuators, by means of only one additional actuator.
In another expedient version, in the event of a fault an actuator which sets a less safety-relevant function of the suspension system also performs the function of a defective actuator that is more important in safety terms. And if appropriate, it can also be taken into account that the intact actuator can no longer (or no longer completely) perform its original function. For example, it is possible to cause a defective steering function of one actuator to be performed by a further actuator which is responsible primarily for setting the camber or the toe of the wheel. The actuator performing the steering function generates an actuating movement with a direction component which is parallel to the actuating direction of the defective actuator responsible primarily for steering. By means of the control, the intact actuator can be activated so that the direction component influencing the steering is as pronounced, or at least approximately as pronounced, as the actuating movement of the steering actuator. Thus, the steering function can continue to be exercised without any safety restriction.
When the function of a defective actuator is assumed by an actuator that is used primarily for another function, the number of all the actuators used corresponds to the number of influenceable possibilities for the movement of the wheel. No additional actuators are required in this version, yet a redundant design is achieved due to function assumption.
It may be expedient, if appropriate, to design two or more actuators such that, in the event of a fault, mutual function assumption is possible. In this general case, when all the actuators are fully operational, the actuating movements of the actuators are normally uncoupled, so that each actuator performs only the primary function assigned to it. In the event of a fault, if there is a partial or complete failure of one or more actuators, the functions of the intact actuators are coupled, while their main functions either continue to be performed at least approximately or are relinquished in favor of the more important functions of the defective actuators. The uncoupling and coupling of the actuators is carried out with the aid of the actuating signals which are generated in the control.
In a preferred embodiment, the force application points of two cooperating actuators are arranged in each case at a distance from the steering axis, so that both actuators can influence the steering angle. If one of the actuators fails, the remaining actuator can be used for steering.
Advantageously, the force application points of the two actuators are also at a distance from a further wheel rotation axis, so that both can generate a torque acting about this wheel rotation axis, in order to set a further degree of freedom of the wheel; in particular camber or toe. If one actuator fails, the remaining operational actuator can assume the steering function, if appropriate with the function for setting the additional degree of freedom of the wheel being reset.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.